Apparatus for Determining the Filterability of Fluids, In Particular of Transmission Oils

ABSTRACT

In an apparatus for determining the filterability of fluids, in particular of transmission oils, having a test filter device ( 21 ), through which a sample amount of the fluid can flow, and a line system which forms a circulation circuit ( 1 ) for the fluid, said line system comprises a foam tester ( 3 ) which receives the sample amount of the fluid, the filter device ( 21 ) and a circulating pump ( 23 ) which removes fluid from the sample amount which is situated in the foam tester ( 3 ) and conveys it through the filter device ( 21 ) and back to the foam tester ( 3 ).

The invention relates to an apparatus for determining the filterability of fluids, in particular of transmission oils, having a test filter means through which a sample amount of the fluid can flow.

To monitor and maintain the condition of technical systems in which fluids are involved as system components, it must be absolutely ensured that the fluids, for example, when they are used as lubricants, maintain the required performance characteristics in the course of operation. Thus, for example, in transmission oils which are routed through cooling and filter means as they pass through systems of circulating lubrication, it is necessary to carry out testing of the filterability of the pertinent oils. Conventionally, for this purpose a sample amount of the oil is routed through a test filter means, preferably such that a plurality of successive passages of the oil through the filter media is undertaken, that therefore a number of filtration cycles are carried out. This also permits determination of the compatibilities between the given types of oil and the filter media. In addition, in this way filter passage and material compatibility between the oil and filter, especially with respect to additives, such as for example anti-foam and wear protection (EP/AW), can be tested. Furthermore the effect of filtration on foam formation can be checked.

As has, however, been shown, there is the danger that for oils which are provided with an anti-foam additive package which does not have sufficient stability in operation, after a longer filtration interval the concentration of the anti-foam additive decreases so that intensified, in some cases harmful, foaming of the oil occurs. Therefore it is necessary to check the oil for foaming behavior after a corresponding number of filtration cycles.

In this respect the object of the invention is to devise a device which within the scope of determining the filterability of fluids, in particular transmission fluids, enables checking of their foaming behavior.

According to the invention, this object is achieved by a device which has the features of claim 1 in its entirety.

While in the past in tests of filterability the foaming behavior was determined separately from the actual filtration cycles by removing secondary samples which were studied separately for foaming behavior from the filtration test bench after completion of the corresponding number of filtration cycles, according to the invention the foam test is integrated directly into the filtration test bench. A series of disadvantages is eliminated in this way.

While in the past the fluid volume in the filtration test bench changed due to removal of a comparatively large amount of the secondary sample, which had a change of the test conditions for the sample, volumes and test conditions thus now remain the same. One exception to this is minor sample removal for optional laboratory studies, such as, for example, special forms of emission spectroscopy. This does not result in any time loss for removal of the secondary sample, transport, the foam test and return of the secondary sample to the filtration test bench. Moreover, there is no danger that external effects (fouling, water and the like) in the handling of the secondary sample could constitute an error source for sensitive test runs.

For the device according to the invention a foam tester is especially well-suited which has a test housing which holds the sample amount of fluid and in which a roamer means which causes mixing of the fluid with air is contained. These foam testers are available for example under the commercial name Flender-Schaumtest [Flender foam test] (A. Friedr. Flender GmbH).

Preferably the line system of the circulation circuit has a return line which leads from the filter means to the test housing of the foam tester and which feeds the fluid below the liquid level of the sample amount into the test housing. This avoids foaming by the backflow of the recirculated oil emerging from the filter means in the operating phases between the actual foam test, that is, in the time intervals of shutdown of the gear pair which is used as the roamer.

Preferably the test filter means is a membrane filter means with one or multiple filter layers, the filter medium preferably corresponding to the filter material, as is used in a technical systems (for example the transmission of a wind power plant) with a condition which is to be monitored by means of the device according to the invention. Alternatively filter elements folded into a star or bag filters and comparable filter arrangements can be used.

The invention will be detailed below using one embodiment shown in the drawings.

FIG. 1 shows a schematic for illustration of one embodiment of the device according to the invention, a Flender foam tester being shown in a side view and a circulation circuit for a fluid which is to be tested for filterability being shown as a block diagram, and

FIGS. 2 and 3 show diagrams in which the results of the testing of two transmission oils carried out with the device according to the invention are shown.

In the embodiment of the device according to the invention shown in FIG. 1, a circulation circuit for a fluid to be tested is designated as a whole as 1. How the device works is explained below using the example of testing a fluid in the form of a transmission oil for the transmission of a wind power plant. The circulation circuit 1 integrates a commercial Flender foam tester 3 which has a test housing 5 with an interior which is dimensioned for holding the desired sample amount of the oil to be tested, in this example one liter. In the test housing there is a gear pair as the roamer means with intermeshing gears 7 and 9 on vertical axles 11 and 13, the axle 13 forming a drive shaft which is driven by an electric motor 15 for the gear 9.

As can be recognized through a viewing window 19 in the test housing 5, the gears 7 and 9 are located at a vertical level in which they are halfway immersed in the fluid level designated as 17, so that the rotary motion of the gears 7 and 9 causes mixing of the oil and air.

As other components the circulation circuit 1 into which the foam tester is integrated has a test filter means 21, a circulation pump 23 in the form of an electric motor-drive geared pump, and a pressure limitation valve 25 which is connected next to the circulation pump 23. The intake side of the circulation pump 23 is connected via a line 27 to the interior of the test housing 5 of the foam tester 3 such that the circulation pump 23 removes fluid from the bottom area of the test housing 5. The pressure side of the pump 23 is connected via a pressure line 29 to the inlet side of the filter means 21 which has an output side which is connected in turn to the test housing 5 of the foam tester 3 via a return line 31, the mouth 33 of the return line 31, as is to be seen from FIG. 1, being located underneath the fluid level 17 in the test housing 5. Instead of the indicated geared pump, other drive devices for the fluid can also be used.

To test the filterability of the pertinent fluid, the test housing 5 is filled with a sample amount of the fluid to be tested, for example with transmission oil in an amount (for example, approximately one liter) such that after filling the circulation circuit 1 (lines, pump, filter) the gears 7 and 9 are halfway immersed in the fluid level 7. Before carrying out a corresponding number of filtration cycles, i.e., before circulating the added “fresh oil”, by operating the foam tester 3, the original foaming behavior is determined, on a scale division on the viewing window 19 the percentage volume change being determined which is established following an operation-specific waiting time after carrying out the foam test.

Then a given number of filtration cycles is carried out by operating the circulation pump 23 in the circulation circuit, here a cycle being defined as the time required for the test oil to be conveyed once through the test filer means 21, viewed statistically. The cycle duration can be computed as the quotient of the fluid volume and the volumetric flow.

After carrying out the desired number of filtration cycles, for example 100 cycles, in turn the circulation process is interrupted and a foam test is carried out in order to determine the change of the foaming behavior. In order to ascertain how the foaming behavior changes after a still longer operating time, i.e., after completing a large number of filtration processes, then a larger number of filtration cycles is carried out, after which the foam tester 3 is restarted in order to determine the foaming behavior which the test oil exhibits after a longer operating time.

FIG. 2 shows the test results determined in the testing of a transmission oil using the percentage volume increase caused by foaming of the test oil. Depending on the kind of oil and the oil category, for example, a volume increase of 15% can be regarded as the highest allowable boundary value.

This boundary value is shown in FIG. 2 by the dot-dash line 35. As is illustrated in FIG. 2 by the lower curve, the test oil before carrying out the filtration cycles has an initial foaming behavior which is far below the boundary value indicated with line 35. As the middle curve shows, foreign behavior can still be assumed even after carrying out a plurality of cycles. This test oil for a longer operating interval, see the upper curve, however, has unsatisfactory foaming behavior, according to a volume increase of more than 15%. The testing of these kinds of oils has thus shown that the test oil contains an insufficiently stable anti-foam additive package. A further variable can also be dictated by temperature control.

Conversely, FIG. 3 shows the test results for a type of oil in which the additives which suppress foaming exhibit unobjectionable operating behavior. All curves (for the start of testing, for a few cycles and for a great many cycles) extend far below the boundary value of the 15% volume increase by foaming which is indicated by line 35. As shown by the respective upper curve for a plurality of cycles, this type of oil has good operating behavior even for a longer operating interval, i.e., filterability is not adversely affected by the anti-foam additives settling on the surface of the filter material; this would results in a decrease in the concentration of these additives and thus excess foam formation. The cycles shown in FIGS. 2 and 3 relative to the triangle symbol used relate to the start of the test, relative to the square symbol the end of the test, and relative to the circular or point indication an instant between the start of the test and the end of the test.

The filter means 21 preferably can have round filter elements in a pressure filter holder. Preferably in this connection filter rounds of the same filter material are used as in the analogous technical system the condition of which is to be monitored. Instead of the indicated round filter elements, folded filter media, bag filters, or the like can be used. Furthermore, it is possible to use the foam tester or the foam test device as an oil tank for the entire device. With the device according to the invention an easily manageable measurement process is specified in order to draw a conclusion about the filterability of media. 

1. An apparatus for determining the filterability of fluids, in particular of transmission oils, having a test filter means (21) through which a sample amount of the fluid can flow, and a line system (27, 29, 31) which forms the circulation circuit (1) for the fluid and which contains a foam tester (3) which holds the sample amount of the fluid, the filter means (21) and a circulation pump (23) which removes fluid from the sample amount located in the foam tester (3) and conveys it through the filter means (21) and back to the foam tester (3).
 2. The device according to claim 1, wherein the foam tester (3) has a test housing (5) which holds the sample amount of fluid and in which a foamer means (7, 9) which causes mixing of the fluid with air is contained.
 3. The device according to claim 2, wherein the roamer means is a meshing gear pair (7, 9) which can be driven and which is partially immersed in the liquid level (17) of the fluid.
 4. The device according to claim 3, wherein the line system of the circulation circuit (1) has a return line (31) which leads from the filter means (21) to the test housing (5) of the foam tester (3) and which feeds the fluid below the liquid level (17) of the sample amount into the test housing (5).
 5. The device according to claim 1, wherein the test filter means is a membrane filter means (21) with one or more filter layers.
 6. The device according to claim 5, wherein the filter means (21) contains filter rounds in a pressure filter holder. 